We’re going to have to live somewhere else eventually, you know. The expression “don’t put all your eggs in one basket” has never been more true when applied to our situation as residents of a single planet on a single solar system. Short-term, we might do something appallingly stupid and nuke ourselves into permanent decline and extinction. We could, in our paltry and underfunded survey of the sky, miss a rogue asteroid whose path would interpose with ours in a most fatal way. Long-term, the ecological damage we’ve inflicted on this planet could make it uninhabitable. Even if we do manage to preserve our Eden, we’re on a time crunch here -- the sun is not immortal, and its death throes several billion years in the future will either cook Earth like a kernel of popcorn or consume it utterly.

That’s to say nothing of the fact that a gamma-ray burst from a distant star could blow off the atmosphere of this planet like the seeds of a dandelion, irradiating us in the process and generally making life on Earth rather nasty. The best part is that we’d have no way to stop it and, since the burst would move nearly the speed of light, practically no warning. It could never happen, or it could happen in the next ten seconds. The likelihood is quite low, but it only needs to happen once for our little experiment in arrogant sentience to come to a quick and brutal end.

Most of us are no good at long-term thinking, even on smaller scales like the duration of our own lifetimes, so these problems are only taken seriously in a kind of sideways, small-scale way. We have small victories -- things like the unmanned rover Curiosity that landed on Mars -- intended almost as practice. Curiosity and prior rovers have data gathering and observation as their primary missions, but their open secret is that they’re anticipating problems that an eventual manned mission would have to face.

The one problem they have difficulty solving is how to measure the long-term effects of space travel on the human body. It’s hard enough to live on this Earth -- what with its storms, extremes of temperatures, roving bands of animals or raiders, and so on -- without having to add things like weightlessness, radiation, meteorites, and a vacuum into the mix. The moon missions offered a starting point, but it only takes a few days to get to the moon, and once you’re there, you can’t stay long. Beyond the moon, Mars and Venus are the next-closest planetary objects, and they’re too far away to simply hop on over. Before we go to either*, we’re going to have to, for reasons of safety and convenience, settle for space stations to be our laboratories.

*Venus might have to wait a while. Mars has a thin atmosphere and is generally inhospitable to life, but you could live on it if you had a reasonably well-constructed shelter. Venus, on the other hand, is covered entirely in clouds of sulfuric acid, has a mean temperature of about 450 degrees, and a surface pressure of 92 times Earth’s. We’ve sent probes there before, but when they enter the atmosphere, we only give some of them parachutes. The others, we expect to be crushed shortly after landing. Venus sucks for colonies. It would make a pretty bitchin’ prison planet, though.

The problems of long-term space travel are legion (aside from the obvious trio of carrying enough food, water, and air for a multi-year trip in a tin can), but let’s examine the issue of living without gravity. You can get around in zero gravity easily enough (with the proper training) and things like eating (easy), drinking (use a straw) and sex (seatbelts recommended but not required) are all possible and even fun. Your internal processes suffer, however, with very little you can actually do about it.

Every second you stand up, you’re working against the gravity of a six-septillion ton planet trying to pull you down. We’ve adapted to this state of affairs because it’s all we’ve really known -- we didn’t grow up on a moon of Jupiter and make our way to Earth. Dealing with this gravity keeps your muscles in shape and prevents them from atrophying. If you’re in space, said muscles don’t have nearly as much to do -- you might push off a wall every once in awhile, but you’re engaging in even the most minor daily muscular stresses.

Astronauts on long space flights start to lose muscle mass, which they can counter by daily treadmill use. Their bone density starts to suffer as well, and this is the real issue, because there’s very little they can do in terms of a routine that they can do to deal with that. How do you maintain your focus on an eight-month mission to the red planet when your own body, freed of its responsibilities, has done the physiological equivalent of going home early for the day? There’s a real risk that astronauts on Mars would be weak as kittens after their extended time in space.

Occasionally, you’ll have the stereotypical “Eureka!” moment in science, where a researcher stumbles upon a flash of insight that reveals an elegant solution to a problem. Mostly, though, said solutions are the result of thousands and thousands of hours of testing -- scientists trying myriad different diets and routines on scores of willing astronauts, wiling away their hours in space trying, in a roundabout way, to make it that much easier for another explorer somewhere down the line to make it to another world with his or her mind and body intact.

Joe DeMartino is a Connecticut-based writer who grew up wanting to be Ted Williams, but you would not BELIEVE how hard it is to hit a baseball, so he gave that up because he writes words OK. He talks about exploding suns, video games, karaoke, and other cool shit at his blog. He can be emailed at jddemartino@gmail.com and tweeted at @thetoycannon. He writes about sports elsewhere. The sports sells better.